With semiconductor devices, in particular with memory devices such as DRAMS (DRAM=Dynamic Random Access Memory or dynamic read-write memory, respectively), a voltage level used internally in the device may differ from an external voltage level used outside the device.
In particular, the internally used voltage level may be smaller than the externally used voltage level—for instance, the internally used voltage level may be 1.8 V, and the voltage level used externally may be 2.5 V.
The reason for this may, for instance, may be that the external voltage supply is subject to relatively strong fluctuations, and, therefore—in order that the device can be operated without fault—has to be converted, by a voltage regulator, to an internal voltage (that is subject to relatively minor fluctuations only and that is regulated at a particular, constant value).
By the use of voltage regulators, a loss of voltage may occur, which may result in the voltage level used internally in the device being smaller than the external voltage level.
An internal voltage level that is reduced vis-à-vis the externally used voltage level has the advantage of reducing power loss in the semiconductor device.
If a lower voltage level is used internally in the device than is used externally, the signals generated internally in the device typically—before being output outside—are conconverted to corresponding, higher-level signals by so-called level converters.
Such level converters may, for instance, an amplifier circuit that includes cross-coupled p- or n-channel field effect transistors.
By using the amplifier circuit, internal, low-level signals generated in the device can leave afflicted with certain delay times—be converted to corresponding higher-level signals.
However, the delay time occurring with a positive edge of an internal signal may differ from the delay time occurring with a negative edge of the internal signal. The result thereof is that the higher-level signals output by the amplifier circuit are distorted.
To compensate for this effect, the signals output by the amplifier circuit may be supplied to a driver stage comprising a plurality of, e.g. two, inverters connected in series.
The inverters are designed such that a compensation of the distortions contained in the signals output by the amplifier circuit is achieved.
The driver stage does, however, result in a relatively high-additional—signal delay; furthermore, the above-mentioned signal distortions may, for instance due to changes in the characteristics of the level converter devices caused by temperature fluctuations, in general be compensated for only incompletely by a level converter of the above-described type.